a. Field of the Invention
The present invention relates to a surgical snare for performing a procedure known as colonoscopic polypectomy.
b. Description of the Prior Art
Various types of surgical snares have been employed for a number of years to remove polyps from the colon and rectum. Advances have been made whereby surgical snares have been introduced through the elongated bore of a colonoscope. A colonscope is a fairly multiconduited tubular member useful for inserting into a bowel for examination thereof internally. It possesses a fiber optics system whereby light may be transmitted to the distal end thereof for illumination of a site. Similarly, the fiber optic system includes the means to view the thusly illuminated site.
The surgical snare comprises an elongated flexible sheath connected at its proximal end to an operating handle. Extending through the sheath is an elongated flexible cable, the proximal end is connected to means in a handle whereby the operating loop can be extended beyond an open end of the sheath and may be withdrawn thereinto. The operating loop terminates as a fold which is that portion that extends beyond the sheath when it is protracted. In other words there is a loop connected to the distal end portion of the cable.
The loop comprises the snare. The loop can be opened or closed by the operator of the snare to the extent that he operates a movable portion of an operating means to extend forwardly or to withdraw the folded portion of the cable.
When the cable is in its protracted position a loop is formed forward and external of the sheath. The loop is formed due to the resiliency of the cable especially due to the fold which tends to want to unfold thereby forming a loop. The operator is thereby in a position to play the loop over and around a polyp required to be removed. The cable may then be retracted resulting in diminishing the overall size of the loop as the cable is withdrawn into the sheath. Closing off the loop entirely will sever the polyp. To prevent bleeding from the blood vessels at the remaining severed surface a coagulating radio frequency current is applied to the cable and thence to the loop as the patient is grounded in a conventional manner. The radio frequency is applied just prior and during the severing procedure.
The deficiencies inherent in the prior art instruments can be identified as follows:
1. A large proportion of the loop must be protracted from the sheath before it can define an open configuration. This characteristic makes it difficult for the operator to effectively adjust the size of the loop to the size of the polyp being removed and to the working area available. A large loop must be formed to remove even a small polyp. In order to open the loop adequately it is often necessary to advance the loop blindly beyond the space within the bowel visible to the operator, a potentially dangerous manuever. The large loop in unwieldy and often difficult to maneuver in a small space.
2. After repeated use the resiliency of the wire loop diminishes and a satisfactory configuration is no longer achieved when the loop is protracted beyond the sheath.
3. The loop can be formed in one plane only which often makes it difficult to maneuver the loop over the polyp.
These deficiencies have been partially overcome by later changes in snare design.
Komiya in U.S. Pat. No. 3,903,892 describes a snare in which the configuration of the loop can be controlled to a limited degree by differential protraction of the two members of the loop, achieved by the use of an elongated spring within the sheath.
Chamness et al in U.S. Pat. No. 4,955,578 described a snare in which the plane of the loop can be altered by rotating the operating loop assembly about its long axis. This snare usually requires a larger sheath than can be accomodated by the commonly used colonoscopes and does not correct the loop configuration deficiencies of the standard snares.
Shinya and Wolf (Hospital Practice, September 1975, Page 72) describe a simple snare consisting of a braided steel wire doubled over and inserted through a Teflon catheter of 2.7 mm. outside diameter. Both segments of the cable extend the full length of the sheath and each segment can be independently protracted or retracted by the fingers of the operator of the snare. This device permits the formation of a loop varying in size from very small to very large, the plane of which can be adjusted from one that is parallel to the axis of the sheath to one that is at right angles to that axis. These capabilities provide a decided advantage in the often difficult task of accurately maneuvering the loop over the head of the polyp. They also make it possible to open the loop and remove it from the polyp if repositioning should seem advisable. However, this device requires the services of a highly trained assistant who must have at his disposal a teaching attachment (auxiliary eyepiece) for the colonoscope. This requirement renders this very versatile snare inaccessable to most endoscopists, who do not have available the services of such a highly trained assistant.